The present invention relates to a transmission, and more particularly, to a transmission suitable for use in working vehicles such as fork lift trucks and the like.
So called constant mesh structures are employed in a transmission for vehicles such as fork lift trucks and the like wherein the speeds range from 10 to 20 Km/h and wherein gear changes between forward and reverse gears often occur. In such constant mesh structures, a synchrohub is fixed on a main shaft between the forward and the reverse gears, which are rotatably supported on the main shaft. Clutch gears are provided integrally on the forward and reverse gears, respectively, corresponding to the synchrohub. A coupling sleeve is slidably engaged with the synchrohub. When gear changing is required, the shift lever is operated to move the shift fork so as to shift the coupling sleeve toward the forward gear or reverse gear. As a result, the forward gear or reverse gear is connected through the coupling sleeve with one of the clutch gears.
In such vehicles, forward or reverse gear changes often occur, and the operation of the gear changes frequently starts while the clutch is released but without the vehicle being stopped. If the vehicle does not stop completely, the main shaft continues to rotate together with the clutch disc, due to the inertia thereof while the gear changing operation is commencing. However, the forward and reverse gears rotate in opposite directions, so that the rotational speed difference between them is relatively large, as compared with the transmission for an average passenger car. For example, the rotational speed difference in such vehicles between the coupling sleeve and the clutch gears may be 5-10 times as large as that in passenger cars. Under such conditions, if the coupling sleeve is forcibly engaged with the clutch gear for the forward or reverse gear, then gear change noise occurs, and the abrasion of the clutch gear and coupling sleeve is high. Sometimes the clutch gears are broken, and also the operational feeling is disagreeable.
If the synchronizing mechanisms generally used for passenger cars are employed in order to overcome such defects, the production cost becomes very high. In addition, because the rotational speed of the synchronized parts of working vehicles is high, with accompanying high abrasion, frequent changing of these expensive parts is required.